The present invention pertains to a device for applying fluid material on a substrate and, in particular, to an application valve for such a device.
In many industrial applications, fluid applying devices are used for intermittent delivery and application of liquids onto various objects (substrates), for example, in order to apply adhesives, coloring materials or the like onto automobile parts, packages, furniture or paper, on whole areas, in beads or in dots. The so-called application head with the valve assembly and nozzle assembly is part of a complex application system which includes a container for the fluid material, a transport pump, and a control unit for controlling and/or regulating the individual components. The substrate can be moved relative to the application head with the help of a transport system, or the application head may be attached to a robot arm, or the like, and can move relative to the substrate.
Intermittent application means that the flow or stream of the fluid material in the supply canal, and thus the emission of the material from the outlet opening of the nozzle assembly, is alternately released or interrupted by intermittent activation of the valve assembly. In this way, an interrupted pattern of material is created on the substrate; that is, for example, dots separated by intervals or interrupted longitudinal beads, or spaced rectangular sections of material when the material is applied on areas.
Particularly in applications where objects are to be moved past the application head at high speed and to have fluid material applied, intermittent interruption of the flow of material is necessary. At high relative speeds between the substrate and the application head and/or to create application patterns with small intervals between individual coated areas or short lengths B in the direction of relative motion B of coated area, the valve assembly must be activated at high switching frequency, or in other words, the valve body, which interrupts the flow of material in the supply canal, must be moved back and forth at high speed and high frequency.
Conventional application heads rely on a coil spring to pre-tension the valve body in the closed position. The fluid material, for example, adhesive, is supplied in an upper area of the main body and then flows through a canal which runs essentially axially in the main body, toward the outlet opening of the outlet canal, and at the same time flowing around the coil spring which is located in the outlet canal. A disadvantage of the known apparatus is that the flow path for the material through the main body is relatively long, which leads to relatively large pressure losses.
An additional known problem is that the adhesive fluid material in the portion of the flow path through and about the coil spring and armature introduces drag that increases as the pressure or viscosity of the adhesive fluid material increases. The drag dramatically slows the movement of the armature for interrupting the flow of adhesive fluid material in the supply canal. As the adhesive fluid material flows through and about the entire length of the coil spring and armature, adhesive fluid materials of relatively high viscosity, in particular, are difficult to apply in accurate amounts due to the high drag experienced by the coil spring and the armature.
The present invention provides an apparatus in which a valve assembly can be switched rapidly and with high frequency so that the flow of material can be interrupted or released with high frequency. The apparatus promotes reliable, intermittent application of materials with high viscosities, especially liquid adhesives.
According to the invention, the apparatus includes a supply canal for supplying material from a source of material, a main body with an outlet canal which communicates with the supply canal and ends in an outlet opening for delivering the material, and with a valve assembly located in the main body for optional interruption of the flow of material in the outlet canal. The valve assembly has a valve seat and a valve body which can move relative to the valve seat, as well as a tensioning device which biases or pre-tensions the valve body in either a closed or open position. A drive unit moves the valve body between a closed position which interrupts the flow of material and an open position which releases the flow of material. The supply canal is located in a lower part of the main body and is connected to the outlet canal. The tensioning device for pre-tensioning the valve body is located in the lower part of the main body.
The apparatus of the invention reduces the effect of pressure variations in the fluid material, especially in the supply canal, on the application of the material and on the activation of the application valve. The total flow path, and thus the pressure loss within the applicator, is significantly smaller than in known devices. Furthermore, impairment of the tensioning device by the fluid material, especially sticking of the tensioning device, which is preferably in the form of a coil spring, can be prevented. Moreover, with the apparatus in accordance with the invention, highly viscous fluids can be applied reliably and high switching frequency of the valve assembly can be realized.
In one embodiment, in which the tensioning device is a coil spring, the valve assembly includes a needle valve with an elongated, needle-like valve body and an essentially ring-shaped projection on the valve body against which the coil spring rests. In the ring-shaped projection are flow canals through which the fluid material can flow, producing a simple design with low resistance to flow.
In accordance with an alternative embodiment, the outlet canal extends in the axial direction with reference to a longitudinal axis of the main body and the supply canal extends essentially in the radial direction in reference to the longitudinal axis of the main body. The supply canal intersects in the outlet canal in the area of the coil spring. This allows a compact construction to be achieved overall and allows sufficient space for connecting hoses or the like for supplying the fluid material.
In an alternative embodiment of the invention the outlet canal is disposed at least partially inside of a sleeve inserted into the main body. A sleeve of this sort is easily manufactured and can be designed in such a way that its fluid mechanics are optimal. Furthermore, the main body can consist of a different material. This optimizes the apparatus and lowers the overall production costs.
In another embodiment of the invention, the drive unit for moving the valve body has an electromagnetic coil arrangement configured to produce a magnetic field which operates on the valve body to move it to the closed or open position. A coil arrangement of this sort can be activated rapidly at high frequencies, so that a high switching frequency can be achieved for the valve assembly. The coil arrangement is easily controlled and eliminates the need for a source of pressurized air, such as is necessary for pneumatically operated valves. The application of force needed to move the valve body can be amplified by locating at least one magnetically active element, preferably in the form of a pole element or flux ring, adjacent to or close to the coil.
According to one aspect of this embodiment, an adjusting element is movable relative to the main body and can be secured in various positions, forming a stop for the movable valve body, so that the stroke of the movable valve body is adjustable. Preferably, the adjusting element has male threading and can be screwed into the main body or into a threaded sleeve which is set into the main body.
The adjusting element may be in the form of a pole piece that is permeable by the magnetic field induced by the coil assembly so that a relatively strong force is generated which acts in the axial direction on the valve body to move the valve body back and forth. In one operating state, the valve body preferably rests directly against the magnetically active adjusting element. The adjusting element may be pre-tensioned relative to the main body by a coil spring.
In accordance with an additional aspect of the invention, an advantage of manufacturing technique results from having the main body made of synthetic material. The other components of the applicator can be embedded, for example, in a cast main body. If the applicator is subject to high mechanical loads, the main body can be enclosed in a housing made of a hardened material, such as a sheet metal.
A separate connecting adapter, with a section of the supply canal, can be attached to the main body and receive a hose connector. This facilitates easy connections and attachments.
In another embodiment of the invention, an electrically-operated dispensing module includes a main body having an outlet canal capable of receiving viscous liquid and an outlet opening for discharging the fluid material flowing through the outlet canal onto the substrate, a pole piece positioned within the main body, and a valve assembly positioned within the outlet canal. The valve assembly has a valve seat and a valve body movable relative to the valve seat between a closed position interrupting the flow of fluid material in the outlet canal by engaging the valve body with the valve seat and an open position releasing the flow of fluid material in the outlet canal to the outlet opening by disengaging the valve body from the valve seat.
The dispensing module further includes an electromagnetic drive unit capable of generating a magnetic field for moving the valve body relative to the pole piece between the closed and open positions and a flux element positioned proximate to the electromagnetic drive. The flux element includes a portion capable of interrupting circumferential electrical current paths therein. As a result, any magnetic field induced by eddy currents in the flux element readily dissipates after the electromagnetic drive is denergized, which permits the dispensing module to be rapidly moved from the open position to the closed position.